DNA Structure
DNA is a double helix of nucleotides held by base pairs.
About this topic
DNA (deoxyribonucleic acid) is a double helix, discovered by Watson and Crick in 1953 using Rosalind Franklin's X-ray data. Each strand is a chain of nucleotides made of a sugar (deoxyribose), a phosphate and a base. The strands run in opposite directions (antiparallel) and are held by hydrogen bonds between bases: A pairs with T, and C with G.
The order of bases forms the genetic code. Complementary base pairing makes copying accurate.
The rungs of the DNA ladder are pairs of bases: adenine always pairs with thymine and cytosine always with guanine, held by hydrogen bonds. The sugar-phosphate backbones run in opposite directions, described as antiparallel. If one strand reads ATTGC, the other must read TAACG. The order of bases along a gene is the code.
Chargaff's rule, that in any DNA the amount of A equals T and of C equals G, was a clue to this pairing. Understanding the structure helped explain how DNA can be copied and how mutations arise. Each human cell contains about two metres of DNA, packed into a nucleus a few micrometres across. A common mistake is thinking RNA and DNA are the same; RNA is single-stranded, has ribose and uses uracil instead of thymine.
Key ideas
- A pairs with T, C pairs with G
- Sugar-phosphate backbone
- Antiparallel strands
Quick check
Use cases: where DNA Structure helps
- Homework: review the key idea behind DNA Structure before you start a problem set.
- Exam revision: use the quick check to test whether you can recall DNA Structure without notes.
- Visual learning: play with the interactive lab to see how DNA Structure changes when you adjust its inputs.
- Teaching a friend: explain DNA Structure in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is DNA Structure?
DNA is a double helix of nucleotides held by base pairs.
What will I learn in DNA Structure?
A pairs with T, C pairs with G. Sugar-phosphate backbone. Antiparallel strands.
Is DNA Structure part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the DNA Structure lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study DNA Structure?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.